HSDPA is a high-speed packet data transmission system for the downlink in a wireless communication system. In HSDPA, a group of user equipments (UE) is scheduled in each Transmission Time Interval (TTI), which is 2 ms long. That is, within the 2 ms duration of a given TTI, a scheduler in the Node B selects a small number of UEs, to which data is to be transmitted in that 2 ms interval. In the next 2 ms interval, the scheduler may select another group of UEs to whom to transmit. Data is transmitted to each of the scheduled UEs via a physical channel called the HS-PDSCH (High-Speed Physical Downlink Shared Channel).
User equipments do not receive advance notice of particular TTIs in which they will be scheduled. Because a given scheduled user lacks such advance knowledge, the Node B must let the scheduled UE know that a particular transmission is meant for him. In HSDPA, this is achieved using a control channel called HS-SCCH (High-Speed Shared Control Channel). At any given time, each scheduled UE will be served by a distinct HS-SCCH channel. The various HS-SSCH channels are distinguished by having different spreading codes.
The HS-SCCH channel contains the unique identity of the user equipment (UE) who is scheduled, along with several parameters that the user will need in order to decode the received transmission. That is, it provides timing and coding information which allows the UE to listen to the HS-DSCH (High-Speed Downlink Shared Channel) at the correct time and using the correct codes. In other words, the HS-SSCH indicates which UE will receive information in a determined TTI.
So the HS-SCCH channel is a fixed rate (60 kbps, SF=128) downlink physical channel used to carry signalling related to HS-DSCH transmission. This High-Speed Shared Control Channel (HS-SCCH):                Carries the key necessary information for HS-DSCH demodulation.        The number of allocated HS-SCCH channels corresponds to the maximum number of users that will be code-multiplexed. Currently the maximum number of the HS-SCCH signals receivable by a user equipment is predetermined as four, so each UE will only need to consider a maximum of four HS-SCCH channels at a given time. The HS-SCCHs that are to be considered are signalled to the UEs under the coverage of a set of Node Bs by the RNC that controls those Node Bs.        Each HS-SCCH block has a three-slot duration that is divided into two functional parts. The HS-SCCH uses half-rate convolutional coding with the two parts of the block encoded separately. For protection, both HS-SCCH parts employ user equipment-specific scrambling to allow each UE to decide whether the detected control channel is actually intended for that particular UE.        The first slot (first part, Part1) carries the time-critical information that is needed to start the demodulation process in due time. Part1 parameters indicate: (i) the codes to de-spread; (ii) if QPSK or 16 QAM is used.        The next two slots (second part, Part2) contain less time-critical parameters. CRC is included to check the validity of the HS-SCCH information and HARQ (hybrid ARQ) process information.        
Once a particular TTI of three slots (2 ms) has been assigned to a UE, the Node B identifies the necessary HS-DSCH parameters. For instance, how many codes are available, if 16 QAM can be used, and what are the UE capability limitations.
The Node B starts to transmit the HS-SCCH two slots before the corresponding HS-DSCH TTI to inform the UE of the necessary parameters.
The UE monitors the HS-SCCHs given by the network, and once the UE has decoded Part1 from an HS-SCCH intended for that UE, it will start to decode the rest of that HS-SCCH and will buffer the necessary codes from the HS-DSCH.
Upon having the HS-SCCH parameters decoded from Part 2, the UE can determine to which ARQ process the data belongs and whether it needs to be combined with data already in the soft buffer.
If the network continues to transmit data for the same UE in consecutive TTIs, the same HS-SCCH will be used.
As indicated before, there is a maximum of four HS-SCCH per cell, which allows having a maximum of four users receiving data in the same TTI. The drawback of having all four channels activated is that they use four SF128 codes, and also too much power since this channel has a very low power control in order to be able to reach all the UEs present in the cell.
Then, the optimised number of HS-SCCH channels depends mainly on the number of codes being used by HS-PDSCH, Release 99 traffic, and HSDPA traffic and its type.
Current implementations are based on a static setting of the number of HS-SCCH, which is not an optimal implementation since the optimal number of channels varies with the data traffic, that is different between different cells and at different times of the day.
If the setting is too high, i.e. too many HS-SCCH channels are enabled versus the current HSDPA traffic requirement, TX power could be wasted; and if it is too low the number of users supported simultaneously could not be enough to serve many low bit rate users in an efficient way.
PCT patent application published WO-A1-2008/050152, incorporated herein by reference, discloses a method of scheduling resources in a communication system which comprises allocating code space for users of a channel controlled by the base station, and allocating the same code space for users of a channel controlled by the network control entity. This document refers to the scheduler, but not to the HS-SCCH channels.
Then US patent publication number 2005171984 (A1), incorporated herein by reference, discloses a comprehensive dynamic management scheme of HS-DSCH channel codes.